I currently have 5 which I maintain everyday and about 20 plus for my clients registered under my name because they trust me so much. 
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: this_feature_currently_requires_accessing_site_using_safari
Currently owning 3, it gets very confusing if you're owning more.
But they're on auto renew each year so I don't have to worry about them unless I'm adding a sub domain.
Ever since 2000 I have owned more than 100 domains. I sold a few which I was offered a good deal. Having such huge hoard of domains I couldn’t manage all while others were not quite productive hence I left a few dozens to expire. So far I only have a few are standing strong. Up to now I only need ten domains that can stand on their own hence I am planning to sell a dozen. However I don’t market them which have caused me to take more than four months now looking for a buyer.